Localized administration of therapeutic agents within a body vessel can be advantageous for treatment of a variety of medical conditions. Although such medical conditions can be treated by the general systemic administration of a therapeutic agent, systemic administration of some therapeutic agents can not only result in the unnecessary absorption of the therapeutic agent by tissue outside an intended point of treatment, but also require administration of a greater dose of the therapeutic agent than necessary to compensate for the dissipated therapeutic agent. Accordingly, the treatment of many conditions requires local delivery of the therapeutic agent to a particular portion of internal body tissue, without dissipating the therapeutic agent to the tissue surrounding the particular portion of tissue.
To aid site-specific localized treatment, percutaneous delivery systems such as medical catheters can be used to deliver a therapeutic agent to the target site within a body vessel with minimal invasiveness. Medical catheters permit the delivery of the therapeutic agent from the medical catheter placed within the body vessel proximate the desired treatment site. The delivery of the therapeutic agent from the medical catheter can occur before, during and/or after a procedure such as percutaneous transluminal coronary angioplasty (PTCA), a technique used to dilate stenotic portions of blood vessels. The medical catheter can be adapted to perform a PTCA procedure and locally deliver the therapeutic agent to the site of the procedure. During PTCA, a medical balloon catheter is threaded into and through a body vessel lumen along a wire guide and positioned at a stenosis or other point of treatment, where the balloon is inflated to dilate the target site of the body vessel lumen. After treatment, the balloon is deflated and the catheter is removed from the target site and the patient's lumen, thereby allowing blood to freely flow through the unrestricted lumen.
At times after PTCA the treated portions of the body vessel can have a reoccurrence of constrictions or blockages. This phenomenon is called restenosis, which is the reoccurrence of stenosis at the treated site within the body vessel that can be caused by the body responding to the surgical procedure. Restenosis of the body vessel commonly develops over several months after the procedure, which can require another angioplasty procedure or a surgical by-pass operation. Proliferation and migration of smooth muscle cells (SMC) from the media layer of the lumen to the intima can cause an excessive production of extra cellular matrices (ECM), which is believed to be one of the leading contributors to the development of restenosis. The extensive thickening of tissues narrows the lumen of the blood vessel, constricting or blocking the blood flow through the vessel.
Therapeutic agents can limit or prevent restenosis. The therapeutic agents can be locally delivered with PTCA from a catheter and/or by placement of a stent configured to release the therapeutic agent after the PTCA procedure. Procedures involving medical balloon catheters can also be used in combination with the placement of stents, synthetic vascular grafts or administration of therapeutic agents, during the PTCA procedure to reduce or eliminate the incidence of restenosis.
Medical balloon catheters have been developed to administer the therapeutic agent locally to tissue while dilating a body vessel. For instance, a medical balloon catheter can include two concentrically arrayed coaxial balloons at the distal end of a double balloon catheter, also called a balloon-inside-a-balloon design. The outer balloon can include one or more perforations or holes to locally administer a therapeutic agent, while the inner balloon provides the dilatation and/or sealing of the body vessel lumen.
Nevertheless, localized administration of therapeutic agents evenly within a body vessel with a double balloon catheter can be difficult. In particular, during administration of the therapeutic agent, more of the therapeutic agent can diffuse out of the outer balloon holes at the proximal end of the outer balloon than from the outer balloon holes positioned nearer the distal end of the outer balloon. This can result in administering the therapeutic agent unevenly along the length of the outer balloon, possibly due to fluid pressure losses between the annular spaces along the length of the balloon due to the wall shear stresses on the fluid flowing between the balloons. Thus, there remains a need for a multiple balloon catheter for expanding a body vessel and locally administering medication evenly to the body vessel for an intended medical application. Also, there remains a need for a multiple balloon catheter for expanding a body vessel and locally administering medication to the body vessel evenly along the length of the balloon catheter to avoid overloading of the therapeutic agent at the proximal end and/or underloading of the therapeutic agent at the distal end of the catheter.